The invention is in particular intended for patients suffering from one of a specific group of eye disorders, such as Macular Degeneration, Stardgardt's disease, cataract, pseudophakia, nystagmus, cornea problems, retinal defects and diabetic retinopathy. These patients are troubled by reduced vision, image distortion and sensitivity to light.
The clinical picture of these patients is generally characterized by progressively decreasing vision which, in combination with their other limitations, causes them great problems over the years. Eventually these patients will not go completely blind. The reduced and distorted vision usually starts in the central area in the fovea of the eye or in the cornea and in a later stage of the syndrome extends to the periphery of the fovea.
An eye disorder that is by far the most common is called Macular Degeneration, abbreviated MD. It is a disorder that concerns the central part of the retina, the macula lutea, also referred to as the yellow spot. Typical of MD is, amongst other things, a central scotoma with image distortion, sensitivity to light and a bilateral, progressive loss of the central field of view, the retinal image and a decrease of the number of cones in comparison with the number of rods. A process may be started whereby the cones—which are mainly located in the centre of the retina—start to die. This results in loss of vision, causing the patient's eyesight to become less and less acute. Distortion and—at a later stage—a central scotoma develops centrally in the patient's field of view.
This process is usually age-related, and many people have to face it, partly due to the proportional increase of the ageing population. Usually the disorder is called or considered to be retinal “wear”. However, there are other forms not covered by the general term “Macular Degeneration”, which forms are not age-related. See FIG. 1 for a view of the image as it is perceived by an MD patient.
Stargardt's disease is one of the eye disorders that cause MD. MD causes damage to the macula, which in turn leads to a decreased visual acuteness. The macula or “yellow spot” is the central part of the retina, which enables a person to see sharply. The macula comprises a large number of cones, the light-sensitive cells that are capable of perceiving contrast and colours and thus enable a person to distinguish details (the central, acute perception), such as recognizing poetry, reading and watching TV. The area around the macula is called the peripheral part, it is this part that enables us to see from the corner of our eyes (peripheral vision). Said peripheral vision enables people to see things to their right and left without turning their head.
Stargardt's disease is caused by a change in a gen, usually the process commences in the seventh year of a person's life. This gen produces a specific protein which functions to remove a harmful substance from the cones. When a person has Stargardt's disease, this process is not carried out properly, as a result of which the cones in the macula gradually die and a person's visual acuteness gradually deteriorates.
In most cases both eyes are affected at the same time, and although a person's visual acuteness can remain constant for some time, there is a possibility of a strong sudden deterioration. In very few cases does Stargardt's disease result in blindness, because the peripheral part of the macula almost invariably remains intact.
Another disorder, called cataract, concerns a clouding of the lens, which may be caused by various factors. Usually the disorder is age-related, but it may also be caused by the intake of cortisons or by diabetes. Transmission of the incoming light through the clouded lens becomes more difficult, so that said light reaches the retina less easily. This leads to a few typical phenomena: vision gradually becomes more blurred. Especially the patient's ability to see far is affected. In most cases, reading is still fairly easy. If the cloudiness is at some places more distinct than at other places, the patient may be troubled by double vision and he or she may be blinded more quickly.
Currently cataract is still treated surgically, and the most recent and most widely used treatment technique is “phaco-emulsification”. The envelope around the lens is surgically opened, the lens is crushed and the remnants are sucked up. Subsequently, an artificial lens is placed in the free space.
Nystagmus concerns involuntary, rhythmic rapid eye movements in both eyes, usually synchronously. In some cases the eyes oscillate like the pendulum of a clock: this phenomenon is referred to as pendulum nystagmus. The phenomenon whereby the speed of movement in one direction is different from that in the other direction is referred to as jerk nystagmus or sawtooth nystagmus. The eyes float away, as it were, and are pulled back with a rapid, jerky movement.
Nystagmus is also referred to as “wobbly eyes” or “vibrating eyes”.
If the patient contracted this disorder at a young age, he will have reduced vision and affected colour vision or, quite the reverse, due to the complete or partial lack of cones and a complete or partial lack of colour vision, the patient's vision will amount to around 10%, which vision is mainly provided by the rods, as a result of which the patient will also be sensitive to light.
A patient who suffers from achromatopsia has no cones in his retina, at least no cones that function. As a result, he is unable to perceive colour and to see sharply, whilst furthermore he is sensitive to an abundance of light.